A switchgear is an integrated assembly of switches, buses fuses and other components used to isolate electrical equipment at an electrical installation, for example, an electrical power sub-station. Switchgear is used to both de-energise equipment to allow work to be done and to clear faults downstream of the switchgear. Switchgear is often housed in a metal cabinet at the installation.
A distinction is made between so called ‘fixed switchgear’ and so called ‘withdrawable switchgear’. In fixed switchgear the main circuit breaker is fastened within the installation by fasteners, for example bolts, and cannot be removed from the installation without using tools to undo the fasteners. In withdrawable switchgear additional constructional features enable the main circuit breaker to be withdrawn from the installation (and put back in) with a minimum usage of tools or with no usage of tools. Accordingly, in a withdrawable switchgear, the main circuit breaker can be removed quickly for maintenance or replacement or to provide easy access to other components in the installation.
FIG. 5 is a schematic illustration of a conventional withdrawable switchgear 30 comprising, a circuit breaker 31 comprising a first breaker contact 31a and second breaker contact 31b, and a cabinet 32 containing busbars 33. The switchgear 30 further comprises a first terminal 34 and a second terminal 35 each comprising a respective electrically insulating housing 34a and 35a. The insulating housing 34a contains an electrical contact 34b connected to a busbar 33 and the insulating housing 35a contains an electrical contact 35b connected to a cable connection 36 which is for connecting to a cable (not shown) routed to a load (not shown).
In FIG. 5, the circuit breaker is shown in the withdrawn position in which there is no electrical connection between the busbar 33 and the load (not shown). In a service position, the breaker 31 is located in the cabinet 32 with the first breaker contact 31a inserted into the first housing 34a engaging the contact 34b and the second breaker contact 31b is inserted into the second housing 35 engaging the contact 35b. In this way, when the breaker is closed (e.g. not tripped) an electrical connection exists between the busbar 33 and the load (not shown) through the breaker 31. This configuration is not compact.
U.S. Pat. No. 3,889,722 describes a plastic insulated switching unit for a multiphase high voltage switchgear. The switching unit comprises an insulating housing defining a cylindrical cavity and fixed ring-shaped contacts at an inside wall of said housing. A drawout switching device comprises a projecting tubular pole, having an operating mechanism. The tubular pole comprises ring-shaped contact pieces mounted on its outside. The switching device is moveable between a fully inserted position and an isolating position. In U.S. Pat. No. 3,889,722 the fixed ring-shaped contacts are each located in a first recess formed in the inner surface of the insulating housing.